The present disclosure is generally related to toners comprising polyester resins, and in embodiments, to toners made by emulsion aggregation (EA) and coalescence processes. The toners herein, in embodiments, are environmentally friendly, as they do not use the endocrine disruptor Bisphenol A. The toners herein, in embodiments, provide improved carbon/oxygen ratios. In addition, the toners herein, in embodiments, exhibit stable charge and low relative humidity sensitivity. In embodiments, the toners comprise a wax, and are useful in oil-less fusing applications (requiring little or no fusing oil for release).
Current polyester based toners are derived from Bisphenol A monomer. Bisphenol-A has been identified as an endocrine disrupter resulting in adverse developmental health effects. Several European Countries, as well as Canada and several U.S. states have targeted the ban for Bisphenol A.
Toners that do not use bisphenol-A polyester resins are known, such as those derived from aliphatic glycols and terephthalic acids. Although these resins may provide the suitable fusing performance, the toners display poor electrical performances due to their hydrophilic nature. As a design rule for obtaining good electrical performance, a successful model that has been used in polyester resins, is to calculate the carbon/oxygen (C/O) ratio of the resin. For example, known toners using Bisphenol A and/or styrene based resins have been shown to have a C/O ratio of from about 4.2 to about 4.95. These toners show stable charge and low RH sensitivity. Previous designs using terephthalic-glycol based resins showed a C/O ratio of from about 2.75 to about 3, and displayed poor electrical and RH sensitivity results. Therefore, it is desirable that the C/O ratio of polyester resins be at least 4.0 or greater, or 4.2 or greater, in embodiments from about 4.2 to about 5.5, to result in stable charge and low RH sensitivity similar to that of styrene-based resins.
Thermal properties are a necessary part of the design of a suitable toner. Toners should be designed to help prevent the occurrence of “hot offset.” The resin useful in the toner should be amorphous, in embodiments, with a glass transition temperature ranging from about 50° C. to about 65° C., in embodiments from about 52° C. to about 60° C. The softening point, as measured by Mettler Softening point apparatus, should be desirable ranges for high gloss application, or for matte applications.
Illustrated in U.S. patent application Publication No. 2008/0236446, the disclosure of which is incorporated herein by reference in its entirety, are toner preparation processes, and more specifically, a process for the preparation of toner including i) generating an emulsion including water and resin containing from about 5 to about 70 percent solids of amorphous polyester resin particles with a particle diameter size of from about 50 to 250 nanometers; (ii) generating an emulsion of crystalline polyester resin particles with a particle diameter size of from about 50 to about 250 nanometers; (iii) aggregating said resulting mixture of amorphous polyester resin particles, crystalline polyester resin particles, and colorant including from about 25 to about 45 weight percent solids dispersion and wax dispersion with a coagulant at a pH of from about 2.5 to about 4, which pH is achieved with a dilute acid, and shearing the resulting mixture with a homogenizer at from about 2,000 to about 10,000 rpm; and (iv) subsequently heating the mixture to a temperature of from about 40° C. to about 55° C. to thereby generate toner aggregates of from about 3 to about 9 microns in diameter; followed by freezing said aggregate size by the addition of alkaline base at a pH of from about 6.3 to about 9, and adding a metal sequestering agent; heating the resulting aggregate composite to a temperature below the onset melting point of the crystalline resin to enable coalescence; decreasing the pH of the mixture from about 5.7 to about 6.3 with an acid or buffer to coalesce the toner components; and thereafter cooling, washing, isolating, and drying the toner product.
Emulsion/aggregation/coalescence processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of each of which are incorporated herein by reference in their entirety, such as U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797; and also of interest may be U.S. Pat. Nos. 5,348,832; 5,405,728; 5,366,841; 5,496,676; 5,527,658; 5,585,215; 5,650,255; 5,650,256; 5,501,935; 5,723,253; 5,744,520; 5,763,133; 5,766,818; 5,747,215; 5,827,633; 5,853,944; 5,804,349; 5,840,462; 5,869,215; 5,863,698; 5,902,710; 5,910,387; 5,916,725; 5,919,595; 5,925,488; 5,977,210; 5,994,020; 6,020,101; 6,130,021; 6,120,967 and 6,628,102, 6,664,015, 6,780,560, 6,818,723, 6,824,944, 6,830,860, 6,849,371, 7,208,253, 7,329,476, 7,402,371, 7,416,827 7,425,398, and 7,442,740.
In addition, the following U.S. patents relate to emulsion aggregation processes of forming toner compositions, the disclosures of each of which are totally incorporated herein by reference in their entirety.
U.S. Pat. No. 5,593,807 describes processes for the preparation of toner compositions including: (i) preparing an emulsion latex comprised of sodio sulfonated polyester resin particles of from about 5 to about 500 nanometers in size diameter by heating said resin in water at a temperature of from about 65° C. to about 90° C.; (ii) preparing a pigment dispersion in a water by dispersing in water from about 10 to about 25 weight percent of sodio sulfonated polyester and from about 1 to about 5 weight percent of pigment; (iii) adding the pigment dispersion to a latex mixture including sulfonated polyester resin particles in water with shearing, followed by the addition of an alkali halide in water until aggregation results as indicated by an increase in the latex viscosity of from about 2 centipoise to about 100 centipoise; (iv) heating the resulting mixture at a temperature of from about 45° C. to about 80° C. thereby causing further aggregation and enabling coalescence, resulting in toner particles of from about 4 to about 9 microns in volume average diameter and with a geometric distribution of less than about 1.3; and optionally (v) cooling the product mixture to about 25° C. and followed by washing and drying.
U.S. Pat. No. 7,402,371 describes a method for forming a low melt toner, the method including: forming a pre-toner mixture including (i) an emulsion resin including a first alkali sulfonated polyester resin and a second alkali sulfonated polyester resin, (ii) a colorant, and (iii) optionally a wax; adjusting the pH of the pre-toner mixture to between about 4 to about 5; homogenizing the pre-toner mixture; forming an aggregate mixture of aggregate toner particles by adding an aggregating agent over a period of from about 10 to about 60 minutes; adjusting the pH of the aggregate mixture to between about 5 and about 7; heating the aggregate mixture to a temperature of from about 50° C. to about 80° C. thereby forming a mixture coalesced toner particles; controlling toner particle size by adjusting the pH of the mixture of coalesced toner particles to between about 5 and about 7; and cooling the mixture of coalesced toner particles to room temperature.
Illustrated in U.S. patent application Publication No. 2008/0107989 is a process for forming particles, including forming a latex by generating an emulsion of a polyester resin initially having an acid value of from about 16 mg/eq KOH to 40 mg/eq KOH; optionally adding thereto a colorant dispersion, a wax dispersion, and/or a surfactant; shearing and adding an aqueous solution of acid until the pH of the mixture is from about 3 to about 5.5, followed by optionally adding an aqueous solution of coagulant; heating to a temperature of from about 30° C. to about 60° C., wherein the aggregate grows to a size of from about 3 to about 20 microns; raising the pH of the mixture to from about 7 to about 9; heating the mixture to about 60° C. to about 95° C.; and optionally decreasing the pH to a range of about 6 to about 6.8.
Therefore, it is desired to provide a toner having a polyester resin, which is not derived from the endocrine disruptor Bisphenol-A. It is further desired to provide a polyester resin toner which has a suitable glass transition temperature, softening point, C/O ratio, improved electrical characteristics, and RH sensitivity. In addition, it is desired to provide a toner that can be used in an oil-less fusing system, requiring little or no fusing oil.